Escherichia coli mastitis in the Dairy Bovine

Mastitis is a continuous concern for dairy producers in the US because of its economic consequences. Coliform mastitis accounts for 20-80% of acute clinical mastitis cases and includes gram-negative pathogens Escherichia coli, Klebsiella and Enterobacter species. Rapid identification of the causative organism is essential to implement a prudent treatment plan. Escherichia coli can be rapidly identified with Eosin Methylene Blue (EMB) agar based on the occurrence of a green-metallic sheen that appears on the surface of the bacterial colonies. Frozen milk samples from which gramnegative bacteria had been isolated and gram-negative bacterial isolates from milk samples were received from eight states. Samples were grown on 5% sheep’s blood agar. Isolated colonies were then plated on EMB agar. Time from inoculation and to first visible green-metallic sheen was recorded. Isolates were identified using (API 20E) biochemical test strips. One hundred and twenty-nine isolates or milk samples were received. Nine species of gram-negative bacteria were identified by the use of biochemical test strips. Of 63 E. coli isolates, 61 were EMB positive, and of 66 non-E. coli gram-negative isolates, 64 were EMB negative, for an intermethod agreement of 96.9% and a κ-value of 93.7% indicating excellent agreement beyond chance between identification of E. coli with biochemical test strips and EMB agar. The minimum and maximum time to first visible sheen were 3.3 hours and 10 hours respectively, for a mean